Credit

Caption

Drug crossing the blood-brain barrier. Illustration of the haematoencephalic barrier between the blood flow (left) and the central nervous system (right). This system regulates the environment (homeostasis) in the brain by separating it from the blood. The blood-brain barrier stops harmful chemicals and bacteria from reaching the brain. Within the blood vessel at left are red blood cells (red) and white blood cells (yellow). Drug molecules (blue) are also seen. Viruses and special types of drugs are able to pass the blood-brain barrier, passing through the holes shown here.